My apologies to Google. I was too harsh. She is very chatty, and often helpful, but she doesn't much care if what she tells you is true or not. And sometimes she'll kiss and tell (at a price). That's hard on trust in a relationship
Do you have Thai spelling for these two products: gypsum, and agricultural lime? My Thai wife first says "Never heard of it" then "Nobody here uses these" then "maybe they have in Surin, who knows?" The article linked is very helpful about how to test and calibrate amount. I just cannot find any around here! I imagine SCG makes both. Prasat is too far away from here, halfway to Cambodia
What they are saying is they don't know whats coming out of your mouth., because its wrong. Gypsum powder is Pung Yip Sum ผงยิปซั่ม The other is elemental hydraulic lime which is calcium oxide. Also called quicklime, or just plain Lime is Phun Khaow ปูนขาว. Bloody English is more ambiguous then Thai would you believe.